Infants with congenital or neonatal herpesvirus infections (HSV or CMV) are at risk for severe morbidity. Impaired herpes-specific immune responses are likely to contribute to this morbidity and, in the case of CMV, to delay in eliminating the virus. We have developed methods for quantitating specific immune responses to herpesviruses accurately and we propose to apply these to infants with congenital or neonatal infections. We shall study infants with a documented history of HSV or CMV infection.